Method of minimizing aldehyde based impurities in a process stream

ABSTRACT

Oxidation of an alkane to an alkanone in a process stream forms aldehyde-based impurities. A method of minimizing the aldehyde-based impurities introduces an amine into the process stream to minimize the aldehyde-based impurities. The amine interacts with the alkanone and the aldehyde-based impurities thereby forming heavy products. The method separates the heavy products from the alkanones to reduce a level of the aldehyde-based impurities. The process stream preferably includes cyclohexyl ketone as the alkanone and n-hexanal as the aldehyde-based impurity. The method is typically involved in synthesis of a caprolactam.

FIELD OF THE INVENTION

The subject invention generally relates to a method of minimizingaldehyde-based impurities in a process stream. More specifically, thesubject invention relates to introducing an amine into the processstream to minimize the aldehyde-based impurities.

DESCRIPTION OF THE RELATED ART

Process streams allow a constant flow of reagents to react together toform desired compounds. Typically, the process streams are used incommercial processes to synthesize the desired compounds on a largescale. For example, oxidation of alkanes to alkanones, or cyclic alkanesto cyclic alkanones, in the commercial processes is completed using theprocess streams. As the alkanes are oxidized to form the alkanones, manyother compounds are also formed including aldehyde-based impurities. Itmay be desirable to separate the aldehyde-based impurities from thealkanones, i.e., from the desired compounds. This is especiallyimportant in the commercial processes that are dependent on purealkanones with little or no impurities.

One such commercial process that is dependent on pure alkanones withlittle or no impurities includes synthesis of a caprolactam. Thesynthesis of 2-azacycloheptanone, a type of caprolactam, includes anoxidation of the cyclic alkane, cyclohexane, to the cyclic alkanone,cyclohexyl ketone, in the process stream. The synthesis also includesforming hydroxylamine in the presence of a platinum catalyst. Thesynthesis further includes reacting the cyclohexyl ketone with thehydroxylamine to form an oxime. The method still further provideschemically rearranging the oxime to form the caprolactam.

To efficiently complete the synthesis of the caprolactam, thealdehyde-based impurities must be separated from the alkanone. If thealdehyde-based impurities are not separated, the synthesis will notproceed with high yield. Methods of separating the aldehyde-basedimpurities from the alkanones, such as those methods used in synthesisof the caprolactam, are known in the art.

A first prior art method of separating the aldehyde-based impuritiesfrom the alkanones only utilizes temperature differences to distill andseparate the aldehyde-based impurities from the alkanones. This firstprior art method is deficient because simply distilling and separatingthe aldehyde-based impurities from the alkanones does not remove all ofthe aldehyde-based impurities. Due to difficulties in removing all ofthe aldehyde-based impurities in practice, a range of between 600 and900 parts of the aldehyde-based impurities per 1 million parts of thealkanone remaining after distillation is not uncommon. Therefore, thefirst prior art method cannot be used in the commercial processes, suchas synthesis of the caprolactam, that are dependent on pure alkanoneswith little or no impurities.

A second prior art method utilizes a basic hydroxide or carbonate toreact with the aldehyde-based impurities and form β-hydroxyaldehydes.The second prior art method separates the P-hydroxyaldehydes from thealkanones through distillation. This second prior art method isdeficient because use of the basic hydroxide or carbonate promotes aself-condensation of the alkanones to produce polymeric alkanones. Fordescriptive purposes only, a chemical reaction schematic of theself-condensation of a representative alkanone, a cyclic alkanone, isillustrated below.

Polymerization of the alkanones renders the alkanones unusable forfurther processing in many commercial processes, such as synthesis ofthe caprolactam. Also, because the second prior art method results in upto a 25% loss of the alkanones to self-condensation, production costsare increased. Further, commercially available alkanes, the startingmaterials of the alkanones, and specifically cyclic alkanes, areparticularly expensive. Therefore, this second prior art method is notefficient for use in the commercial processes due to increasedproduction costs.

A prior art method of minimizing aldehyde-based impurities in a processstream, representative of the second prior art method generallydescribed above, is disclosed in G.B. Patent App. No. 2,028,329. The'329 application discloses reacting the basic hydroxide or carbonate,such as sodium hydroxide or sodium carbonate, with the aldehyde-basedimpurities present in a process stream including cyclic alkanones. Thebasic hydroxide or carbonate reacts with the aldehyde-based impuritiesto form the β-hydroxyaldehydes that can be separated by distillation.Yet, addition of the basic hydroxide or carbonate to the process streampromotes the self-condensation of the cyclic alkanones to produce thepolymeric cyclic alkanones. As described above, polymerizing thealkanones renders the alkanones unusable for further processing in manycommercial processes, such as synthesis of the caprolactam. The '329application does not disclose use of amines to minimize thealdehyde-based impurities in a process stream or any method that wouldnot promote the self-condensation of the alkanones. Therefore, themethod disclosed in the '329 application is not suitable for use in thecommercial processes, such as the synthesis of caprolactam, that aredependent on pure alkanones with little or no impurities.

Another prior art method of minimizing aldehyde-based impurities in aprocess stream, also representative of the second prior art method, isdisclosed in Jap. Pat. Pub. No. JP 49-011848. The '848 publicationdiscloses adding ammonium hydroxide to a solution of n-hexanal andcyclopentanone. The ammonium hydroxide reacts with the n-hexanal to formthe 0-hydroxyaldehyde. The '848 publication does not disclose the use ofamines to minimize aldehyde-based impurities in the process stream.Specifically, the ammonium hydroxide is a basic hydroxide and is not anamine. Therefore, the ammonium hydroxide promotes the self-condensationof the cyclic alkanones, as described above. Therefore, the methoddisclosed in the '848 publication is not suitable for use in thecommercial processes, such as synthesis of the caprolactam, that aredependent on pure, monomeric cyclic alkanones with little or noimpurities.

The various prior art methods described above are not suitable for usein the commercial processes, such as synthesis of the caprolactam, for avariety of reasons. These prior art methods have not been optimized foruse in the commercial processes to reduce the production costs. Thebasic hydroxide or carbonate such as ammonium hydroxide, sodiumhydroxide, or sodium carbonate, when added to the alkanones, promote theself-condensation of the alkanones. Any self-condensation of thealkanones reduces useable products and increases the production costs.Also, distilling and separating the aldehyde-based impurities from thealkanones does not easily eliminate all of the aldehyde-based impuritiesin practice. Therefore, neither of the prior art methods can be used incost efficient commercial processes that are dependent on pure alkanoneswith little or no impurities.

SUMMARY OF THE INVENTION AND ADVANTAGES

The subject invention provides a method of minimizing aldehyde-basedimpurities in a process stream. The process stream includes an alkanoneand the aldehyde-based impurities. The method includes the step ofintroducing an amine into the process stream to form a heavy product.The method also includes the step of separating the alkanone from theheavy product.

The method of minimizing the aldehyde-based impurities in the processstream, according to the subject invention, is used to decreaseindustrial production costs. The method utilizes the amines to formheavy products that are separated from the alkanones. By forming heavyproducts, the amines significantly reduce levels of the aldehyde-basedimpurities in the process stream. The amines also minimizeself-condensation of the alkanones which, ultimately, decreases overallproduction costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar graph illustrating a percentage formation of a heavyproduct as a function of certain processing conditions;

FIG. 2 is a bar graph illustrating n-hexanal reduction as a function ofcertain processing conditions;

FIG. 3 is a bar graph illustrating n-hexanal and heavy productconcentration as a function of pH;

FIG. 4 is a three-dimensional bar graph illustrating n-hexanal reductionas a function of time, heat, and molar equivalents of diethylenetriamine(DETA);

FIG. 5 is a three-dimensional bar graph illustrating n-hexanal reductionas a function of time, heat, and molar equivalents oftriethylenetetramine (TETA);

FIG. 6 is a three-dimensional bar graph illustrating n-hexanal reductionas a function of DETA addition, TETA addition, and heat;

FIG. 7 is a three-dimensional bar graph illustrating n-hexanal reductionas a function of certain processing conditions at a pH of 8; and

FIG. 8 is a line graph illustrating a percentage of n-hexanal reductionas a function of pH and amine type.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A method of minimizing aldehyde-based impurities in a process stream isprovided. The process stream of the subject invention includes analkanone and the aldehyde-based impurities. The alkanone in the processstream is a desired product of an oxidation of an alkane. The oxidationof the alkane produces the alkanone, an alcohol, and the aldehyde-basedimpurities, in addition to non-aldehyde based impurities such asperoxides, ethers, and diols.

Preferably, the process stream includes a cyclic alkanone as a desiredproduct of an oxidation of a cyclic alkane. If the method of the subjectinvention includes the cyclic alkanone, the cyclic alkanone can be usedin synthesis of a caprolactam, which can be polymerized to form a nylonfinal product. Any aldehyde-based impurities present with the cyclicalkanone in the process stream can contaminate the synthesis of thecaprolactam and reduce commercial viability of the caprolactam.Therefore, the aldehyde-based impurities are preferably minimized.

Synthesis of the caprolactam includes reacting the cyclic alkanone withan amine to form an oxime. The oxime chemically rearranges to form thecaprolactam. One example of the caprolactam includes2-azacycloheptanone. The caprolactam can be polymerized to form thenylon final product which is commercially sold. A sample chemicalsynthetic scheme for synthesis of the caprolactam is illustrated below.

To efficiently complete synthesis of the caprolactam, the aldehyde-basedimpurities must be separated from the cyclic alkanone. If thealdehyde-based impurities are not separated, the synthesis will notproceed with high yield.

The cyclic alkanone that is used to form the caprolactam is preferablypresent in the process stream. If included in the process stream, thecyclic alkanone preferably includes, but is not limited to, cyclohexylketone. However, the cyclic alkanone may also include cyclopentanones,cycloheptanones, cyclooctanones, and combinations thereof. Thecyclohexyl ketone can be either substituted or unsubstituted. Ifunsubstituted, the cyclohexyl ketone is commonly referred to ascyclohexanone. For descriptive purposes only, a chemical structure ofunsubstituted cyclohexyl ketone (i.e., cyclohexanone) is illustratedbelow.

In addition to the alkanone present in the process stream, the alcoholmay also be present in the process stream, originating from theoxidation of the alkane. The alcohol that may be present in the processstream preferably includes, but is not limited to, a cyclic alcohol.Most preferably, the alcohol, if present, includes cyclohexyl alcohol.For descriptive purposes only, a chemical structure of cyclohexylalcohol is illustrated below.

The aldehyde-based impurities that reduce the commercial viability ofthe caprolactam and that are present in the process stream include, butare not limited to, a hexanal. Typically, the aldehyde-based impuritiesinclude n-hexanal. For descriptive purposes only, a chemical structureof n-hexanal is illustrated below.

The method of minimizing aldehyde-based impurities in the process streamgenerally includes the steps of introducing the amine into the processstream to form a heavy product and separating the alkanone from theheavy product. The step of separating the alkanone from the heavyproduct is discussed below in greater detail.

Preferably, the amine introduced into the process stream includesmonomeric amines, polymeric amines, and combinations thereof. Theterminology “polymeric amine” includes any molecule including[—RN—(CR₂)_(m)—NR—]_(n), wherein R includes a hydrogen or a hydrocarbongroup including any straight chain, branched, or cyclic hydrocarbon, mincludes any integer preferably of from 1 to 10, more preferably of from2 to 6, and most preferably of from 2 to 3, and n includes any integerpreferably of from 1 to 10, more preferably of from 2 to 6, and mostpreferably of from 2 to 3. It is contemplated that the terminology“polymeric amine” also includes a molecule having any type of polymericbackbone having amine functionality on the polymeric backbone. Mostpreferably the amine includes ethylenediamine, diethylenetriamine(DETA), triethylenetetramine (TETA), and combinations thereof. That is,only one amine is necessary to introduce into the process stream, but acombination may be introduced into the process stream. For descriptivepurposes only, chemical structures of ethylenediamine, DETA, and TETA,are shown below, respectively.

The amine is preferably introduced into the process stream in an amountof from 0.1 to 10, and most preferably of from 0.5 to 3 molarequivalents of the amine compared to the aldehyde-based impurities.

The amine can be introduced into the process stream at various points.Preferably, the amine is introduced into a process vessel or a processline, such as a distillation tower, after the alkanone and thealdehyde-based impurities are formed from the oxidation of the alkane.As such, the distillation tower includes the alkanone and thealdehyde-based impurities when the amine is introduced.

Introducing the amine into the process stream may include the step ofinteracting the amine with the aldehyde-based impurities to form theheavy product. The heavy product formed from interacting the amine withthe aldehyde-based impurities includes an imine. The imine has a higherboiling point than either the alkanone or the aldehyde-based impurities.Therefore, if desired, the higher boiling point of the imine can beexploited for distillation purposes.

The step of interacting the amine may also include the step ofchemically reacting the alkanone with the aldehyde-based impurities toform an alkylenyl alkanone as the heavy product. Without intending to belimited by any particular theory, it is believed that the amine mayfacilitate forming the alkylenyl alkanone. Preferably, if the cyclicalkanone is included in the process stream, the cyclic alkanone willchemically react with the aldehyde-based impurities to form an alkylenylcyclic alkanone.

The terminology “alkylenyl cyclic alkanone” refers to a chemicalcompound that includes a cyclic alkanone moiety represented asO═C_(m)R_(n)— and an alkylenyl moiety represented as —C_(k)R_(p).Referring to the cyclic alkanone moiety, O═C_(m)R_(n)— includes a cyclicmolecule wherein m includes any integer of from 3 to 10, n includes anyinteger of from (2m minus 4) to (2m minus 3), and R includes a hydrogengroup, an alkyl or alkenyl group having up to 6 carbon atoms, andcombinations thereof. Referring now to the alkylenyl moiety, —C_(k)R_(p)includes a linear alkylenyl molecule wherein k includes any integer offrom 2 to 10, p includes any integer of from (2k minus 1) to (2k), and Rincludes a hydrogen group, an alkyl or alkenyl group having up to 6carbon atoms, and combinations thereof.

Typically, if formed, the alkylenyl cyclic alkanone includes, but is notlimited to, an alkylenyl cyclic hexanone. Without intending to belimited by any particular theory, it is believed that if the cyclohexylketone is reacted with the n-hexanal, a specific alkylenyl cyclichexanone, 2-hexylidene-cyclohexanone, will be formed. Representativechemical formulas of 2-hexylidene-cyclohexanone include O═C₆H₈═C₆H₁₂ andO═C₆H₉—C₆H₁₁ depending on where a double bond resides.

For descriptive purposes only, a chemical structure of2-hexylidene-cyclohexanone is illustrated below.

Like the imine, the alkylenyl alkanone also has a higher boiling pointthan either the alkanone or the aldehyde-based impurities. As such, thehigher boiling point of the alkylenyl alkanone may also be exploited fordistillation purposes.

The amine may be introduced into the process stream by injection. If theamine is injected into the process stream, it is preferred that theamine is injected into the distillation tower, as introduced above.

Referring now to the step of separating the alkanone from the heavyproduct, i.e., the imine and/or the alkylenyl alkanone, the step mayinclude the step of distilling the heavy product and the alkanone. Ifthe heavy product and the alkanone are distilled, it is preferred thatthe step of distilling the heavy product and the alkanone includes thestep of distilling at a temperature of from 150° C. to 170° C. and morepreferably of from 155° C. to 165° C.

In commercial applications, it is most preferred that the process streamundergoes a series of distillations in multiple distillation towers toadequately separate the alkanone from the heavy product. If the processstream undergoes the series of distillations, a first distillation in afirst distillation tower, without the amine, may remove a portion of thealdehyde-based impurities as a tops product. The terminology “topsproduct” refers to a compound removed from a top of the distillationtower. While a portion of the aldehyde-based impurities may be removedas the tops product, the alkanone may remain in a bottom of the firstdistillation tower and be removed as a bottoms product. The terminology“bottoms product” refers to a compound removed from the bottom of thedistillation tower. In the first distillation, the process stream ispreferably distilled at a temperature of from 120° C. to 140° C. andmore preferably of from 128° C. to 132° C.

To aid in minimizing the n-hexanal in the process stream in the bottomof the first distillation tower, the amine may be introduced into thebottom of the first distillation tower. As explained above, if the amineis introduced into the first distillation tower, the amine maychemically react with the alkanone to form the imine, and the alkanonemay chemically react with the aldehyde-based impurities to form thealkylenyl alkanone as the heavy products, respectively. If the amine isintroduced into the bottom of the first distillation tower, the processstream including the alkanone, any remaining aldehyde-based impurities,and the heavy products preferably flows as the bottoms product into asecond distillation tower for a second distillation.

If the second distillation occurs in the second distillation tower, theprocess stream, at this point, preferably includes only the alkanone andthe heavy products. It is to be understood that remaining aldehyde-basedimpurities may be unavoidably present in the process stream due toincomplete removal as the tops product in the first distillation orincomplete chemical reaction with the alkanone. Preferably, purealkanone is removed as the tops product from a top of the seconddistillation tower and the process stream flows as the bottoms productinto a bottom of the third distillation tower. In the seconddistillation tower, the process stream is preferably distilled at atemperature of from 150° C. to 170° C. and more preferably of from 155°C. to 165° C.

If the process stream flows into the third distillation tower, theprocess stream preferably includes only the heavy products. It is to beunderstood that remaining aldehyde-based impurities and remainingalkanone may continue to be unavoidably present in the process streamwith the heavy products. If the process stream is distilled in the thirddistillation tower, the heavy products preferably remain in the bottomof the third distillation tower. It is contemplated that the heavyproducts may flow as bottom products into other distillation towers foradditional distillation, if necessary.

In another embodiment of the subject invention, the subject inventionmay include the step of adjusting a pH of the process stream at variouspoints in the method. If the pH of the process stream is adjusted, it ispreferably adjusted to from 2 to 7. More preferably, the pH is adjustedto from 3 to 5. The step of adjusting the pH of the process stream mayinclude the step of adding an acid to the process stream. Preferably theacid includes, but is not limited to, an organic acid. Most preferablythe acid includes formic acid.

Optionally, the process stream including the amine may be heated atvarious points in the method. Without intending to be bound by theory,it is believed that heating the process stream increases a kineticchemical reaction of the aldehyde-based impurities and the alkanone,thus aiding in minimizing the aldehyde-based impurities. If the processstream is heated, the process stream is preferably heated to from 130°C. to 170° C. and more preferably of from 130° C. to 150° C.

The method, according to the subject invention, that minimizesaldehyde-based impurities in the process stream yields multipleadvantages, including decreasing industrial production costs. The methodutilizes the amine to form the heavy products. As explained above, theformation of the heavy products is beneficial because it allows forseparation of the heavy products from the pure alkanone. By forming theheavy products, the amine significantly reduces levels of thealdehyde-based impurities in the process stream, which includes thealkanone. The amine also minimizes possible self-condensation of thealkanones, which would raise the industrial production costs throughloss of the desired alkanone.

Referring now to FIG. 1, addition of potassium hydroxide to a 50:50mixture of the cyclohexyl ketone and the cyclohexyl alcohol isillustrated as a control representing the prior art of the addition ofthe potassium hydroxide to the cyclic alkanones. The addition of thepotassium hydroxide to the mixture greatly increases the formation ofthe heavy products including the self-condensation product of the cyclicalkanone and a β-hydroxyaldehyde, as disclosed in the prior art. FIG. 1also illustrates that addition of the DETA and the TETA to the 50:50mixture of the cyclohexyl ketone and the cyclohexyl alcohol includingthe n-hexanal greatly decreases the formation of the heavy productsthereby decreasing the self-condensation product of the cyclohexylketone and reducing production costs.

Referring now to FIG. 2, addition of the potassium hydroxide to a 50:50mixture of the cyclohexyl ketone and the cyclohexyl alcohol includingthe n-hexanal is illustrated as a control representing the prior art ofthe addition of the potassium hydroxide to the cyclic alkanones. Theaddition of the potassium hydroxide to the mixture totally removed then-hexanal in the mixture. FIG. 2 also illustrates that addition of theDETA and the TETA to the mixture greatly decreased the n-hexanalconcentration in the mixture. Therefore, addition of the DETA or TETA tothe mixture is effective in reducing the aldehyde-based impurities inthe process stream.

In both FIGS. 1 and 2, the terminology “Initial” indicates that no aminewas added to the 50:50 mixtures of the cyclohexyl ketone and thecyclohexyl alcohol. The terminology “After DETA addition” indicates that1.5 molar equivalents of the DETA to the n-hexanal was added to 50:50mixtures of the cyclohexyl ketone and the cyclohexyl alcohol. Theterminology “After TETA addition” indicates that 1.5 molar equivalentsof the TETA to the n-hexanal was added to 50:50 mixtures of thecyclohexyl ketone and the cyclohexyl alcohol. The terminology “After KOHindicates” that 1.5 molar equivalents of potassium hydroxide to then-hexanal was added to 50:50 mixtures of the cyclohexyl ketone and thecyclohexyl alcohol, as disclosed in the prior art. In all of theaforementioned conditions, the mixtures were refluxed for 10 minutesafter addition of the amine to the 50:50 mixture, and gas chromatographymeasurements were taken after 10 minutes of reflux of the 50:50mixtures.

Referring now to FIG. 3, addition of the formic acid to 50:50 mixturesof the cyclohexyl ketone and the cyclohexyl alcohol including then-hexanal is illustrated. The addition of the formic acid adjusts the pHof the mixtures to 2, 3, 4, or 5. FIG. 3 also shows that a decrease inpH results in a decrease in formation of the heavy products and adecrease in the n-hexanal concentration in the mixtures. Therefore, alower pH of the mixtures may result in decreased production costs thatwould result from loss of the cyclic alkanone.

In FIG. 3, the terminology “5” indicates the formic acid was added to a50:50 mixture of the cyclohexyl ketone and the cyclohexyl alcohol toadjust the pH to 5. 1 molar equivalent of the DETA to the n-hexanal wasadded to the mixture. The terminology “4” indicates the formic acid wasadded to a 50:50 mixture of the cyclohexyl ketone and the cyclohexylalcohol to adjust the pH to 4. 1 molar equivalent of the DETA to then-hexanal was added to the mixture. The terminology “3” indicates theformic acid was added to a 50:50 mixture of the cyclohexyl ketone andthe cyclohexyl alcohol to adjust the pH to 3. 1 molar equivalent of theDETA to the n-hexanal was added to the mixture. The terminology “2”indicates the formic acid was added to a 50:50 mixture of the cyclohexylketone and the cyclohexyl alcohol to adjust the pH to 2. 1 molarequivalent of the DETA to the n-hexanal was added to the mixture. In allof the aforementioned conditions, gas chromatography measurements weretaken after addition of DETA to the 50:50 mixtures.

Referring now to FIGS. 4 and 5, approximately 400 ppm of the n-hexanalwas added to 50:50 mixtures of the cyclohexyl ketone and the cyclohexylalcohol such that a degradation of the n-hexanal could be measured viagas chromatography measurements. The 50:50 mixtures were adjusted to apH of 6 with addition of the formic acid. The DETA and the TETA wereadded to the 50:50 mixtures in FIGS. 4 and 5, respectively. The DETA andthe TETA were added to the 50:50 mixtures under reflux in 0.5, 1, 1.5,2, and 2.5 molar equivalents to the n-hexanal. Gas chromatographymeasurements were taken at times zero, after 10 minutes of reflux beforeamine addition, at times zero after the DETA or the TETA addition, andat times 3, 6, 10, and 30 minutes after the DETA or the TETA addition.FIGS. 4 and 5 also show the n-hexanal reduction as a function of time,heat, and molar equivalents of the DETA or the TETA. FIGS. 4 and 5 alsoshow a substantial decrease in the n-hexanal concentration in themixtures after addition of the DETA or the TETA. Therefore, upon pHadjustment, addition of the amine and addition of heat, thealdehyde-based impurities in the process stream are reduced, thuslowering production costs.

Referring now to FIG. 6, approximately 400 ppm of the n-hexanal wasadded to 50:50 mixtures of the cyclohexyl ketone and the cyclohexylalcohol such that a degradation of the n-hexanal could be measured viagas chromatography measurements. The 50:50 mixtures were adjusted to apH of 6 with addition of the formic acid. The mixture was separated intomultiple samples, the DETA or the TETA was added to the samples, andsome samples were heated. FIG. 6 depicts a small reduction in then-hexanal concentration with only addition of heat. FIG. 6 also depictsa larger reduction in the n-hexanal concentration with addition of theDETA or the TETA and optional heat. Therefore, upon pH adjustment,addition of the amine and addition of heat, the aldehyde-basedimpurities in the process stream are reduced, thus lowering productioncosts.

Referring now to FIG. 7, a reduction in the n-hexanal concentration withaddition of the DETA or the TETA and optional heat is illustrated.Approximately 400 ppm of the n-hexanal was added to 50:50 mixtures ofthe cyclohexyl ketone and the cyclohexyl alcohol such that a degradationof the n-hexanal could be measured via gas chromatography measurements.The 50:50 mixtures were unadjusted to a pH of 8. The mixture wasseparated into multiple samples, the DETA or the TETA was added to thesamples, and some of the samples were heated. FIG. 7 depicts a smallreduction in the n-hexanal concentration with only addition of heat.FIG. 7 also depicts a larger reduction in the n-hexanal concentrationwith addition of the DETA or the TETA and optional heat. Therefore, uponaddition of the amine and addition of heat, the aldehyde-basedimpurities in the process stream are reduced, thus lowering productioncosts.

Referring now to FIG. 8, the DETA and the TETA effectively reduce then-hexanal concentration in a process stream including cyclohexyl ketoneand n-hexanal. The n-hexanal was added to 50:50 mixtures of thecyclohexyl ketone and the cyclohexyl alcohol such that a degradation ofthe n-hexanal could be measured via gas chromatography measurements. The50:50 mixtures were adjusted to a pH of 3.1, 4.5, 5.6, and 8 withaddition of the formic acid. 3 molar equivalents of different amines tothe n-hexanal were added to the mixtures. Gas chromatographymeasurements were taken before and after 60 minutes of reflux of themixtures. Therefore, FIG. 8 shows that DETA and TETA are the mosteffective amines for reducing the aldehyde-based impurities in theprocess stream, thus maximizing the reduction of production costs.

The following examples generally illustrate the nature of the inventionand are not to be construed as limiting the invention. Unless otherwiseindicated, all parts are given as parts per million.

EXAMPLES

The method of minimizing aldehyde-based impurities in the process streamincluding the alkanone and the aldehyde-based impurities includesintroducing the amine into the process stream to form the heavy product.The amine interacts with the alkanone and the aldehyde-based impuritiesto form the heavy product, and it is contemplated that more than oneheavy product may be formed. The heavy product is separated from thealkanone, preferably through distillation.

According to the subject invention, the amines were added to 50:50mixtures of cyclohexyl ketone and cyclohexyl alcohol includingn-hexanal. The amines interacted with the n-hexanal to form the imine.The cyclohexyl ketone interacted with the n-hexanal, in the presence ofthe amine, to form 2-hexylidene-cyclohexanone. TABLE 1 n-HexanalReduction as a Function of DETA Added 4.6 Equivalents of DETA 8.8equivalents of DETA 13.4 equivalents of DETA Added; pH = 4.6 Added; pH =4.5 Added; pH = 4.5 n- % n- n- % n- n- % n- Hexanal Time Hexanal HexanalTime Hexanal Hexanal Time Hexanal [ppm] (h) Reduction (ppm) (h)Reduction (ppm) (h) Reduction 415 Before 0 415 Before 0 415 Before 0Addition Addition Addition 53 0.1 87.2 35 0.1 91.6 26 0.1 93.7 50 0.5 8831 0.5 92.5 22 0.5 94.7 49 12 88.2 29 12 93 20 12 95.2

Table 1 shows n-hexanal reduction in a 50:50 mixture of cyclohexylketone and cyclohexyl alcohol including 415 parts per million ofn-hexanal at time 0. A pH of the mixture was adjusted with addition offormic acid. Table 1 also shows DETA added in three quantities toidentical samples of the mixture. The samples were stirred at roomtemperature and gas chromatography measurements of the samples weretaken at times 0, 0.1, 0.5, and 12 hours after addition of DETA. TABLE 2n-Hexanal Reduction as a Function of DETA Added DETA Added; pH = 8; RoomTemperature; n-Hexanal [ppm] 1 Molar 2 Molar 3 Molar 4 Molar 5 MolarTime (h) Equiv. Equiv. Equiv. Equiv. Equiv. Before 324 324 324 324 324Addition 0.1 123 105 94 88 84 0.5 114 100 89 84 80 1   106 93 86 78 7912   86 78 77 72 70

Table 2 shows n-hexanal reduction in a 50:50 mixture of cyclohexylketone and cyclohexyl alcohol including 324 parts per million ofn-hexanal at time 0. A pH of the mixture was unadjusted at 8. Table 2also shows DETA added in five quantities to five identical samples in 1,2, 3, 4 and 5 molar equivalents to n-hexanal. The samples were stirredat room temperature and gas chromatography measurements of the sampleswere taken at times 0, 0. 1, 0.5, 1, and 12 hours after addition ofDETA. TABLE 3 n-Hexanal Reduction as a Function of DETA Added DETAAdded; pH = 4.5; Room Temperature; n-Hexanal [ppm] 1 Molar 2 Molar 3Molar 4 Molar 5 Molar Time (h) Equiv. Equiv. Equiv. Equiv. Equiv. Before305 305 305 305 305 Addition 0.1 48 34 35 30 32 0.5 38 36 34 32 29 1  38 35 33 31 30 12   36 32 27 23 22

Table 3 shows n-hexanal reduction in a 50:50 mixture of cyclohexylketone and cyclohexyl alcohol including 305 parts per million ofn-hexanal at time 0. A pH of the mixture was adjusted to 4.5 withaddition of formic acid. Table 3 also shows DETA added in fivequantities to five identical samples in one, two, three, four, and fivemolar equivalents to n-hexanal. The samples were stirred at roomtemperature and gas chromatography measurements of the samples weretaken at times 0, 0.1, 0.5, 1, and 12 hours after addition of DETA.TABLE 4 n-Hexanal Reduction as a Function of TETA Added TETA Added; pH =8; Room Temperature; n-Hexanal [ppm] Time 1 Molar 2 Molar 3 Molar 4Molar 5 Molar (h) Equiv. Equiv. Equiv. Equiv. Equiv. Before 324 324 324324 324 Addition 0.1 198 142 125 102 94 0.5 174 127 108 95 88 1   176115 101 92 82 12   194 131 96 83 87

Table 4 shows n-hexanal reduction in a 50:50 mixture of cyclohexylketone and cyclohexyl alcohol including 324 parts per million ofn-hexanal at time 0. A pH of the mixture was unadjusted at 8. Table 4also shows TETA added in five quantities to five identical samples in 2,3, 4 and 5 molar equivalents to n-hexanal. The samples were stirred atroom temperature and gas chromatography measurements of the samples weretaken at times 0, 0.1, 0.5, 1, and 12 hours after addition of TETA.TABLE 5 n-Hexanal Reduction as a Function of TETA Added TETA Added; pH =4.5; Room Temperature; n-Hexanal [ppm] Time 1 Molar 2 Molar 3 Molar 4Molar 5 Molar (h) Equiv. Equiv. Equiv. Equiv. Equiv. Before 318 318 318318 318 Addition 0.1 47 38 31 32 27 0.5 31 35 30 30 25 1   33 30 28 3025 12   45 34 27 24 26

Table 5 shows n-hexanal reduction in a 50:50 mixture of cyclohexylketone and cyclohexyl alcohol including 318 parts per million ofn-hexanal at time 0. A pH of the mixture was adjusted to 4.5 withaddition of formic acid. Table 5 also shows TETA added in fivequantities to five identical samples in 1, 2, 3, 4 and 5 molarequivalents to n-hexanal. The samples were stirred at room temperatureand gas chromatography measurements of the samples were taken at times0, 0. 1, 0.5, 1, and 12 hours after addition of TETA. TABLE 6 n-HexanalReduction After 60 Minutes Reflux as a Function of Amine Added pH = 3.1pH = 4.5 % n- % n- Amine (3 molar Initial Final Hexanal Initial FinalHexanal equiv.) ppm ppm Reduct. ppm ppm Reduct. Hexamethylene 320 74 77360 0 100 Diamine Cyclohexylamine 283 94 67 254 44 83 Hexylamine 296 4884 312 84 77 Phenylhydrazine 292 224 24 307 218 29 Isobutylamine 270 6469 273 23 92 Octylamine 276 200 28 273 206 25 Nonylamine 208 178 80 20934 84 DETA 250 18 93 260 15 94 TETA 344 24 93 375 21 95

Table 6 shows percent n-hexanal reduction in 50:50 mixtures ofcyclohexyl ketone and cyclohexyl alcohol including n-hexanal at time 0.A pH of the mixtures was adjusted to 3.1 or 4.5 with addition of formicacid. Table 6 also shows amines added to nine samples in 3 molarequivalents to n-hexanal. Gas chromatography measurements of the sampleswere taken before and after 60 minutes of reflux of the samples. TABLE 7n-Hexanal Reduction After 60 Minutes Reflux as a Function of Amine AddedpH = 5.6 pH = 8 % n- % n- Amine (3 molar Initial Final Hexanal InitialFinal Hexanal equiv.) ppm ppm Reduct. ppm ppm Reduct. Hexamethylene 305153 50 280 213 24 Diamine Cyclohexylamine 207 104 50 191 185 3Hexylamine 322 79 74 300 281 73 Phenylhydrazine 342 303 12 324 323 0Isobutylamine 285 81 76 246 128 48 Octylamine 306 218 29 312 245 22Nonylamine 207 35 84 210 131 38 DETA 255 20 92 251 25 90 TETA 301 17 95270 31 89

Table 7 shows percent n-hexanal reduction in mixtures of 50:50 mixturesof cyclohexyl ketone and cyclohexyl alcohol including n-hexanal. A pH ofthe mixtures was adjusted to 5.6 or 8 with addition of formic acid.Table 7 also shows amines added to nine samples in 3 molar equivalentsto n-hexanal. Gas chromatography measurements of the samples were takenbefore and after 60 minutes of reflux of the samples. TABLE 8 n-Hexanaland Cyclohexyl Ketone Reduction as a Function of Amine Type % Cyclic %n- Boiling Alkanone Hexanal Amine FW Pt (° C.) Reduction ReductionCyclohexyl N/A N/A <5% 0 Ketone + Cyclohexyl Alcohol Diphenylamine169.23 302 0 0 Melamine 126.12 N/A 0 4 Aniline 93.13 184 0 5Cyclohexylamine 99.18 134 <5% 5 Acetamide 59.07 221 0 6 Octylamine129.25 175-177 <5% 22 Hexamethylene 116.21 204 <5% 24 Diamine Nonylamine143.27 201 <5% 38 Isobutylamine 73.14 64-71 <5% 48 Hexylamine 101.19131-132 <5% 73 TETA 146.24 266-267 0 89 DETA 103.17 199-209 0 90

Table 8 shows percent n-hexanal and cyclohexyl ketone reduction in 50:50mixtures of cyclohexyl ketone and cyclohexyl alcohol including 300 partsper million n-hexanal. Table 8 shows the amines added to twelve samplesin 3 molar equivalents to n-hexanal. The samples were refluxed forthirty minutes. After thirty minutes of reflux of the samples, gaschromatography measurements of the samples were taken.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.Obviously, many modifications and variations of the subject inventionare possible in light of the above teachings, and the invention may bepracticed otherwise than as specifically described.

1. A method of minimizing aldehyde-based impurities in a process streamcomprising an alkanone and the aldehyde-based impurities, said methodcomprising the steps of: introducing an amine into the process stream toform a heavy product; and separating the alkanone from the heavyproduct.
 2. A method of minimizing aldehyde-based impurities in aprocess stream as set forth in claim 1 wherein the step of introducingthe amine comprises the step of interacting the amine with thealdehyde-based impurities to form the heavy product.
 3. A method ofminimizing aldehyde-based impurities in a process stream as set forth inclaim 2 wherein the step of interacting the amine further comprises thestep of chemically reacting the alkanone with the aldehyde-basedimpurities to form an alkylenyl alkanone as the heavy product.
 4. Amethod of minimizing aldehyde-based impurities in a process stream asset forth in claim 1 wherein the amine is selected from the group ofethylenediamine, diethylenetriamine, triethylenetetramine, andcombinations thereof.
 5. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 1 wherein the aminecomprises diethylenetriamine.
 6. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 1 wherein the aminecomprises triethylenetetramine.
 7. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 4 wherein thealdehyde-based impurities comprise n-hexanal.
 8. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 7wherein the alkanone comprises a cyclic alkanone.
 9. A method ofminimizing aldehyde-based impurities in a process stream as set forth inclaim 8 wherein the cyclic alkanone comprises cyclohexyl ketone.
 10. Amethod of minimizing aldehyde-based impurities in a process stream asset forth in claim 9 wherein the step of separating the alkanone fromthe heavy product comprises the step of distilling the heavy product andthe alkanone.
 11. A method of minimizing aldehyde-based impurities in aprocess stream as set forth in claim 10 wherein the step of distillingthe heavy product and the alkanone comprises the step of distilling theheavy product and the alkanone at a temperature of from 155° C. to 165°C.
 12. A method of minimizing aldehyde-based impurities in a processstream as set forth in claim 1 wherein the aldehyde-based impuritiescomprise n-hexanal.
 13. A method of minimizing aldehyde-based impuritiesin a process stream as set forth in claim 1 wherein the alkanonecomprises a cyclic alkanone.
 14. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 13 wherein thecyclic alkanone comprises cyclohexyl ketone.
 15. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 1wherein the step of introducing the amine comprises the step ofinjecting the amine into the process stream.
 16. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 15wherein the step of injecting the amine into the process streamcomprises the step of injecting the amine into a distillation tower. 17.A method of minimizing aldehyde-based impurities in a process stream asset forth in claim 1 wherein the step of separating the alkanone fromthe heavy product comprises the step of distilling the heavy product andthe alkanone.
 18. A method of minimizing aldehyde-based impurities in aprocess stream as set forth in claim 17 wherein the step of distillingthe heavy product and the alkanone comprises the step of distilling theheavy product and the alkanone at a temperature of from 150° C. to 170°C.
 19. A method of minimizing aldehyde-based impurities in a processstream as set forth in claim 1 wherein the step of introducing the aminefurther comprises the step of introducing the amine in an amount of from0.1 to 10 molar equivalents of the amine compared to the aldehyde basedimpurities.
 20. A method of minimizing aldehyde-based impurities in aprocess stream as set forth in claim 1 further comprising the step ofadjusting a pH of the process stream.
 21. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 20wherein the step of adjusting the pH of the process stream comprises thestep of adding an acid to the process stream.
 22. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 1further comprising the step of heating the process stream to atemperature of from 130° C. to 150° C.
 23. A method of minimizingaldehyde-based impurities in a process stream comprising cyclohexylketone and n-hexanal, said method comprising the steps of: introducingan amine into the process stream to form a heavy product; and distillingthe cyclohexyl ketone from the heavy product.
 24. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 23wherein the step of introducing the amine comprises the step ofinteracting the amine with the n-hexanal to form the heavy product. 25.A method of minimizing aldehyde-based impurities in a process stream asset forth in claim 24 wherein the step of interacting the amine furthercomprises the step of chemically reacting the cyclohexyl ketone with then-hexanal to form an alkylenyl cyclic hexanone as the heavy product. 26.A method of minimizing aldehyde-based impurities in a process stream asset forth in claim 23 wherein the amine is selected from the group ofethylenediamine, diethylenetriamine, triethylenetetramine, andcombinations thereof.
 27. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 23 wherein the stepof introducing an amine comprises the step of injecting the amine into adistillation tower.
 28. A method of minimizing aldehyde-based impuritiesin a process stream as set forth in claim 23 wherein the step ofdistilling the cyclohexyl ketone from the heavy product comprisesdistilling the heavy product and the cyclohexyl ketone at a temperatureof from 150° C. to 170° C.
 29. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 26 wherein the stepof distilling the cyclohexyl ketone from the heavy product comprisesdistilling the heavy product and the cyclohexyl ketone at a temperatureof from 155° C. to 165° C.
 30. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 23 wherein the stepof introducing the amine further comprises the step of introducing theamine in an amount of from 0.1 to 10 molar equivalents of the aminecompared to the n-hexanal.
 31. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 23 furthercomprising the step of adjusting a pH of the process stream.
 32. Amethod of minimizing aldehyde-based impurities in a process stream asset forth in claim 23 further comprising the step of heating the processstream to a temperature of from 130° C. to 150° C.
 33. A method ofminimizing aldehyde-based impurities in a process stream used insynthesis of caprolactam, the process stream comprising cyclohexylketone and n-hexanal, said method comprising the steps of: introducingan amine into the process stream to form a heavy product; and distillingthe cyclohexyl ketone from the heavy product.
 34. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 33wherein the step of introducing the amine comprises the step ofinteracting the amine with the n-hexanal to form the heavy product. 35.A method of minimizing aldehyde-based impurities in a process stream asset forth in claim 34 wherein the step of interacting the amine furthercomprises the step of chemically reacting the cyclohexyl ketone with then-hexanal to form an alkylenyl cyclic hexanone as the heavy product. 36.A method of minimizing aldehyde-based impurities in a process stream asset forth in claim 33 wherein the amine is selected from the group ofethylenediamine, diethylenetriamine, triethylenetetramine, andcombinations thereof.
 37. A method of minimizing aldehyde-basedimpurities in a process stream as set forth in claim 33 wherein the stepof introducing an amine comprises the step of injecting the amine into adistillation tower.
 38. A method of minimizing aldehyde-based impuritiesin a process stream as set forth in claim 33 wherein the step ofdistilling the cyclohexyl ketone from the heavy product comprises thestep of distilling the cyclohexyl ketone and the heavy product at atemperature of from 150° C. to 170° C.
 39. A method of minimizingaldehyde-based impurities in a process stream as set forth in claim 36wherein the step of distilling the cyclohexyl ketone from the heavyproduct comprises the step of distilling the cyclohexyl ketone and theheavy product at a temperature of from 155° C. to 165° C.
 40. A methodof minimizing aldehyde-based impurities in a process stream as set forthin claim 33 wherein the step of introducing the amine further comprisesthe step of introducing the amine in an amount of from 0.1 to 10 molarequivalents of the amine compared to the n-hexanal.
 41. A method ofminimizing aldehyde-based impurities in a process stream as set forth inclaim 33 further comprising the step of adjusting a pH of the processstream.
 42. A method of minimizing aldehyde-based impurities in aprocess stream as set forth in claim 33 further comprising the step ofheating the process stream to a temperature of from 150° C. to 170° C.